Solar cells are devices that convert light energy into electrical energy by the photovoltaic effect. There is currently a high demand for solar cells, because solar cells have many applications. For example, solar cells are used for powering small devices like calculators. Furthermore, solar cells are increasingly being used in vehicles and satellites. Solar cells also have the potential of becoming state-of-the-art power plants, since solar cell technology is a technology branch favored by society. Society favors solar cell technology because the electricity produced by solar cells is renewable ‘clean’ electricity.
Solar cells include a semiconductor material that is used to absorb photons and generate electrons via the photovoltaic effect. One semiconductor material typically used for manufacturing solar cells is silicon. In solar cells, silicon can be used either as mono or polycrystalline silicon.
State-of-the-art silicon solar cells typically include a set of individual silicon plates, each with a size about 15×15 centimeters (cm). Such state-of-the-art solar cells have various disadvantages, however. Due to the large size of the individual silicon plates, the backside of these individual silicon plates are electrically connected using bus bars. The application of the bus bars to the silicon plates is performed by high-temperature diffusion processes, which consume large amounts of energy. High-energy usage during the manufacture of solar cells reduces the cost effectiveness of the solar cells. Furthermore, since bus bars are non-laminar backside contacts, the electrical contacting of the backside of solar cells is not optimal.
The typically large size of the individual plates results in another disadvantage: solar cells are usually connected in series in modules, creating an additive voltage. The reason for connecting solar cells—i.e. individual plates—in series is to minimize electrical resistance losses resulting from the transport of electricity through electrical lines. However, assuming a given limited total area of a solar cell panel having a set of individual plates, just a limited number of individual plates can be used within the solar cell panel, due to the large size of the individual plates. Furthermore, to reach high operation voltages many individual plates have to be connected in series. For example, a typical individual solar cell plate only delivers a voltage of 0.6 volts (V). To obtain a typical operation voltage of a solar cell panel of 66 V, about 100 individual silicon plates have to be connected in series, which requires—in the case where state-of-the-art sized solar cell plates are used—a large amount of space, which is often not available.
In addition, the individual current delivered from one individual state of the art sized solar cell plate is rather high: assuming again the typical size of a standard silicon plate that is 156×156 millimeters (mm), the total area of such a plate is 243 square cm. A typical plate delivers a power of 3.6 watts (W), which at a conversion efficiency of 15% and a typical output voltage of 0.6 V corresponds to a current of 6 amps (A). However, since individual bus bars are used to connect the backside of the solar cell plates, the bus bars have to be designed in a highly robust manner to withstand such high currents. This also increases the costs of design and manufacturing of solar cells.